VESSELS within the wall of retinal vessels have not hitherto been recognized. In general, only the walls of vessels with a caliber greater than 1 mm. are provided with vasa vasorum, the latter arising from adjacent small arteries and forming a dense capillary network in the adventitia. Even in larger arteries they do not penetrate farther than the external layers of the media. They are more abundant in the veins and here penetrate deeper, into the intima, and may even drain the lumen (Maximow and Bloom1).
In studying the retina in bulk after clearing in glycerin, I have, however, observed capillaries in the walls of diseased retinal vessels (Loewenstein,2 1946). I supposed at first that this capillary system represented unknown vasa vasorum, and therefore for years I hesitated to publish my results. It was not until I came across the work of Winternitz, Thomas and Le Compte,3
LOEWENSTEIN A. INTRAMURAL VASCULAR SYSTEM (VASA VASORUM?) IN RETINAL VESSELS. Arch Ophthalmol. 1948;39(1):9-26. doi:10.1001/archopht.1948.00900020012002